As illustrated in Figure 4, shot gathers of the pseudo-primaries
are similar to those of the original dataset. We now
migrate the pseudo-primary dataset by shot-profile, downward-continuation migration.
We use Fourier finite difference Ristow and Ruhl (1994) as our wavefield extrapolation operator for the migration.
Figure 6 compares the image from the primary-only dataset (NFS),
the image from the original dataset (FS), and the image from
the pseudo-primaries, which consists of primaries (from first-order multiples) and multiples (from
higher-order multiples).
Figure 6a shows the migration result of primaries,
Figure 6b shows the migration result of the original dataset
and Figure 6c shows the migration result of pseudo-primaries.
The pseudo-primary image is noisier than the images from the primaries only and the original dataset.
This is caused by the noise from the cross-correlation and first-order multiples in the
pseudo-primary gathers.
In the image obtained by migrating the pseudo-primaries (Figure 6c),
the salt body is clearly imaged, and reflectors below the salt are also well imaged.
However the reflectors below 20,000 ft are contaminated by first-order multiples in the pseudo-primaries,
which are similar to those in the original-dataset image (Figure 6b).

image
Figure 6 Comparison of migration results for (a) the primaries only,
(b) the original dataset (primaries+multiples) and (c) the pseudo-primary dataset.